Refinement of the crystal structure of low temperature Li 3VO 4 and analysis of mean bond lengths in phosphates, arsenates, and vanadates

Abstract

Low-temperature (β II ) Li 3 VO 4 is orthorhombic with a = 6.3259 ± 12, b = 5.4460 ± 8, and c = 4.9469 ± 9 Å and space group, Pmn 2 1 . The structure, refined by least squares to a final ω R = .092, is isotypic with that β II Li 3 PO 4 . It can be described as an ordered wurtzite structure with rows of Li(1) atoms alternating with rows of Li(2) V Li(2) atoms along [100]. All cations are tetrahedrally coordinated with mean distances 〈Li(1)−0〉 = 1.969 Å, 〈Li(2)−O〉 = 1.995 Å, and 〈V O〉 = 1.717 Å. An analysis of mean tetrahedral distances in 62 phosphates, 21 arsenates, and 22 vanadates resulted in values of 1.537 ± 0.009 Å, 1.683 ± 0.010 Å and 1.721 ± 0.012 Å, respectively. A regression analysis of mean bond distance with average cation electronegativity shows a low correlation. However, if the mean distances are corrected for mean oxygen coordination, a high correlation exists between corrected bond distances (effective ionic radii) and mean electronegativity. This correlation suggests that the bond strength of nontetrahedral cations affects to some degree the mean and, therefore, the individual tetrahedral bond distances in phosphates, arsenates, and vanadates.